High Energy Physics
Assistant Professor
Department of Physics
College of William and Mary
300 Ukrop Drive
Williamsburg, VA 23185
Office: Small Hall, 320a
1 (757) 221-5522
makordosky@wm.edu
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William and Mary High Energy Physics |
Mike Kordosky Assistant Professor Department of Physics College of William and Mary 300 Ukrop Drive Williamsburg, VA 23185 Office: Small Hall, 320a 1 (757) 221-5522 makordosky@wm.edu |
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NOTE: I am looking for a talented student to study neutrino interactions (MINERvA experiment) and/or neutrino oscillations (MINOS). See below for details.
I am searching for a postdoctoral reasearcher to work on MINOS and MINERvA see here for details.
I'm an experimental particle physicist studying weak interactions, neutrino scattering and neutrino oscillations. Neutrinos interact only via the weak force and consequently are the most poorly understood particles in the Standard Model. Neutrinos also have the capacity to surprise us: we only discovered that they have mass during the mid- 1990's. I am also interested in hadronic interactions and the way in which our uncertain knowledge of some hadronic processes influences the precision of current and future neutrino experiments. In particular, I'm interested in calorimetry of single particles and neutrino induced hadronic showers. In addition, I'm interested in the way in which hadrons form from an energetic quark (e.g., one that has been struck by a neutrino) inside nuclei. I work on two experMINOSiments, both running as part of the neutrino program at Fermi National Accelerator Laboratory. The experiments are:
The Main Injector Neutrino Oscillation Search (MINOS) measures the way in which neutrinos change flavor as they propagate through space. This phenomenon, known as "neutrino oscillations", can only occur if neutrinos are massive and provides a window on sector of the Standard Model which hasn't been measured before. Neutrinos had a significant effect on the evolution of our universe and it's possible that they are responsible for the slight imbalance of matter over anti-matter in our universe. Neutrinos also form some component of the dark matter in our universe, though probably not the dominant one.
Oscillations occur due to mixing between the weak and mass eigenstates. The former are created in weak interactions and are identified according to the type of charged lepton produced when the neutrino undergoes charged current scattering. The latter are the eigenstates of the free-particle Hamiltonian. The two sets of eigenstates are related by a unitary mixing matrix called the PMNS matrix:
In principle, if neutrinos have mass, we can write one set of eigenstates as a superposition of the other (Greek indices indicate flavor):
as a consequence, a neutrino (with energy E) produced as a particular flavor in a weak interaction has some probability to be observed as having a different flavor after traveling some distance L. For example, MINOS is particularly interested in studying muon neutrino disappearance:
By measuring the rate of muon neutrino disappearance as a function of the neutrino energy the experiment can determine part of the mixing matrix (U&mu 3)) and the difference in squared masses of the second and third mass eigenstates.
The experiment is done by creating a beam of (mostly) muon-neutrinos at Fermilab and then directing them toward two detectors. The first detector (the "Near Detector") is on-site and measures the contents of the beam before the neutrinos have traveled very far. The second detector (the "Far Detector") is 735km away in the Soudan Underground Laboratory, an decommissioned iron mine in northern Minnesota.
The detectors are iron/scintillator tracking/sampling calorimeters and are magnetized to measure the momentum and charge of muons via their curvature. The figure at the right shows the most recent neutrino event measured in the Far Detector (try clicking the figure).
The oscillation analysis is done by measuring the rate of muon neutrino interactions as a function of energy in both the Near and the Far Detectors. The Near Detector is close enough to the neutrino source that no oscillations are expected to have occurred. The Near Detector therefore provides the crucial benchmark on the neutrino flux and cross-sections, both of which are not well known a priori. The Far Detector is located far enough away from the source to allow the muon neutrinos to "oscillate away". Data from the Near Detector are used to predict what we should see at the Far Detector if oscillations do not occur. A reduction in the muon neutrino event rate as a function of energy is a sign of oscillations allowing us to measure the mixing parameters. Results from two years of data-taking are shown below.
We observe muon neutrino disappearance according to the following parameters:
MINOS is currently taking data and will continue through 2010 at least. The main focus of the experiment is to improve the muon-neutrino disappearance measurement, search for sub-dominant muon-neutrino to electron-neutrino transitions (see my colleague Tricia Vahle's page), search for evidence of "sterile" neutrinos, and measure neutrino cross-sections in the Near Detector. I am in charge of the latter effort, which includes a measurements of the total muon-neutrino scattering cross-section, the structure functions F2 and xF3, the quasi-elastic cross-section, charm quark production (via di-muons) and a search for neutral-current coherent pion production.
Because neutrinos only interact weakly we know relatively little about them. Nevertheless, neutrino oscillation experiments rely on observing neutrino interactions in order to measure squared-mass differences and the elements of the PMNS matrix. As neutrino-oscillation experiments become more and more precise the need for a corresponding improvement in our understanding of neutrino interactions becomes acute. Much of the data on neutrino interactions at a few GeV (the region interesting for oscillations) comes from bubble chamber experiments carried out during the 1970's and 80's. Bubble chambers are able to measure interactions in exquisite detail, but the experiments suffered from low event rates and poorly understood neutrino beams. MINERvA is a new experiment designed to remedy this situation.
MINERvA is a next generation neutrino scattering experiment consisting of a central scintillator tracker, used to define the neutrino interaction vertex, surrounded by electromagnetic and hadronic calorimeters to measure particle energies. The detector will sit upstream of the MINOS Near Detector, which it will use to measure the energy and momentum of muons. The clever design of this relatively small and low-cost detector will allow it to resolve the details of neutrino interactions much like a bubble chamber (compare the MINERvA event on the right with the bubble chamber photo above). The intense, relatively well understood, NuMI beam will allow us to measure neutrino cross-sections with an precision that is orders of magnitude better than previous experiments.
MINERvA is currently being constructed, with much effort going on here at W&M (see my colleague Jeff Nelson's page) . I am in charge of commissioning the "Tracking Prototype", a 1/5 copy of MINERvA which will take cosmic-ray data during the summer of 2008. This detector is the venue where the various components of the experiment will be integrated, the first place we'll measure particle tracks, and the first detector we will have to calibrate. If all goes well the cosmic-ray running may be followed by neutrino data taking during the fall.